There are people who will totally turn away from Christianity now because their belief in this man was unfounded, and will now be led astray.

It would do well for Mr. Camping to reflect on Matthew 18:6:

"But whoso shall cause one of these little ones that believe on me to stumble, it is profitable for him that a great millstone should be hanged about his neck, and that he should be sunk in the depth of the sea."